kvserver: replicate enqueue on span config update is expensive

[kvoli]

Describe the problem

In #100349, we began enqueuing replicas (into the replicate queue) upon receiving span config updates. The problem is, in clusters with a larger number of replicas per node, the overhead of enqueuing replicas is significant—and occurs regularly, every 10 minutes when the PTS changes.

Expected behavior

Replicas are enqueued into the replicate queue, when there is a span config change which would cause a replication/lease change. The overhead of this enqueuing is less noticeable on nodes with 100k+ leaseholders.

Additional data / screenshots

PTS record updated on span configs every 10 minutes, which causes a spike in CPU due to ShouldPlanChange called on enqueuing into the replicate queue.

Environment:
Affects master, release-23.1 and release-23.1.9-rc

Jira issue: CRDB-30613